1. Technical Field
The present invention relates to a variable wavelength interference filter, an optical filter device, an optical module, and an electronic apparatus.
2. Related Art
In the past, there has been known a variable wavelength interference filter having reflecting films disposed on respective surfaces of a pair of substrates, the surfaces being opposed to each other, across a gap (a distance between the reflecting films) of a predetermined amount (see, e.g., JP-A-7-243963).
The optical resonator (the variable wavelength interference filter) described in JP-A-7-243963 is provided with a glass substrate having a recessed section formed on the surface thereof, and a diaphragm substrate blocking up the recessed section, and the diaphragm substrate is bonded so as to block up the recessed section of the glass substrate. Further, reflecting films opposed to each other and electrodes opposed to each other are respectively disposed on the bottom of the recessed section and the surface of the diaphragm substrate opposed to the recessed section. Further, the diaphragm substrate has a thick-wall section with a predetermined thickness and a thin-wall section thinner than the thick-wall section disposed in an area opposed to the recessed section, and by applying a voltage between the electrodes, the thin-wall section is deflected to thereby move the thick-wall section back and forth with respect to the recessed section.
Incidentally, in such a variable wavelength interference filter as described in JP-A-7-243963, there has been a problem that when displacing the thick-wall section of the diaphragm substrate toward the glass substrate, the air between the diaphragm substrate and the glass substrate acts as a resistance, and thus the time until the vibration of the thick-wall section stops is increased, and the response is degraded.
In contrast thereto, there has been considered a configuration of reducing the pressure of a space between the diaphragm substrate and the glass substrate to thereby reduce the air resistance (see, e.g., JP-A-2008-241738).
In the variable-shape mirror of JP-A-2008-241738, a thin mirror is housed inside a package kept in a reduced-pressure state. The variable-shape mirror is provided with a plurality of stationary electrodes opposed to the thin mirror, and by applying a voltage between each of the stationary electrodes and the thin mirror, the shape of the thin mirror is changed due to the electrostatic attractive force.
As described above, by housing the variable wavelength interference filter described in JP-A-7-243963 in the package with the reduced inside pressure described in JP-A-2008-241738, it becomes possible to improve the response in displacing the thick-wall section. However, in some cases, the time after displacing the thick-wall section and until the vibration of the thick-wall section stops to thereby make it possible to take out the light with a target wavelength is not sufficiently improved simply by driving the variable wavelength interference filter under the reduced-pressure environment.
Specifically, when applying the voltage between the electrodes of the variable wavelength interference filter described in JP-A-7-243963 to thereby displace the thick-wall section, the spring force of the thin-wall section, and the spring force (the air spring force) due to the air between the diaphragm substrate and the glass substrate act on the thick-wall section, and the vibration occurs. Here, the resistance due to the air spring is reduced by evacuating the air between the thick-wall section and the glass substrate to an outside space, and in some cases, even after the vibration of the thick-wall section stops, the air fails to completely evacuate to the outside space, and the resistance due to the air spring remains. In this case, there arises a problem that it results that the gap amount of an inter-reflecting film gap fluctuates until the resistance due to the air spring vanishes, and the time until the stable state in which the light with the target wavelength can be taken out occurs is increased.